Polycrystalline diamond compacts or inserts often form at least a portion of a cutting structure of a subterranean drilling or boring tools; including drill bits (fixed cutter drill bits, roller cone drill bits, etc.) reamers, and stabilizers. Such tools, as known in the art, may be used in exploration and production relative to the oil and gas industry. Polycrystalline diamond compacts or inserts may also be utilized as percussive inserts on percussion boring or drilling tools. A variety of polycrystalline diamond percussive compacts and inserts are known in the art.
A polycrystalline diamond compact (“PDC”) typically includes a diamond layer or table formed by a sintering process employing high temperature and high pressure conditions that causes the diamond table to become is bonded or affixed to a substrate (such as cemented tungsten carbide substrate), as described in greater detail below. Optionally, the substrate may be brazed or otherwise joined to an attachment member such as a stud or to a cylindrical backing, if desired. A PDC may be employed as a subterranean cutting element mounted to a drill bit either by press-fitting, brazing, or otherwise coupling a stud to a recess defined by the drill bit, or by brazing the cutting element directly into a preformed pocket, socket, or other receptacle formed in the subterranean drill bit. In one example, cutter pockets may be formed in the face of a matrix-type bit comprising tungsten carbide particles that are infiltrated or cast with a binder (e.g., a copper-based binder), as known in the art. Such subterranean drill bits are typically used for rock drilling and for other operations which require high abrasion resistance or wear resistance. Generally, a rotary drill bit may include a plurality of polycrystalline abrasive cutting elements affixed to the drill bit body.
A PDC is normally fabricated by placing a cemented carbide substrate into a container or cartridge with a layer of diamond crystals or grains positioned adjacent one surface of a substrate. A number of such cartridges may be typically loaded into an ultra-high pressure press. The substrates and adjacent diamond crystal layers are then sintered under ultra-high temperature and ultra-high pressure (“HPHT”) conditions. The ultra-high pressure and ultra-high temperature conditions cause the diamond crystals or grains to bond to one another to form polycrystalline. In addition, as known in the art, a catalyst may be employed for facilitating formation of polycrystalline diamond. In one example, a so-called “solvent catalyst” may be employed for facilitating the formation of polycrystalline diamond. For example, cobalt, nickel, and iron are among examples of solvent catalysts for forming polycrystalline diamond. In one configuration, during sintering, solvent catalyst comprising the substrate body (e.g., cobalt from a cobalt-cemented tungsten carbide substrate) becomes liquid and sweeps from the region adjacent to the diamond powder and into the diamond grains. Of course, a solvent catalyst may be mixed with the diamond powder prior to sintering, if desired. Also, as known in the art, such a solvent catalyst may dissolve carbon. Such carbon may be dissolved from the diamond grains or portions of the diamond grains that graphitize due to the high temperatures of sintering. When the solvent catalyst is cooled, the carbon held in solution may precipitate or otherwise be expelled from the solvent catalyst and may facilitate formation of diamond bonds between abutting or adjacent diamond grains. Thus, diamond grains become mutually bonded to form a polycrystalline diamond table upon the substrate. The solvent catalyst may remain in the polycrystalline diamond layer within the interstitial pores between the diamond grains. A conventional process for forming polycrystalline diamond cutters, is disclosed in U.S. Pat. No. 3,745,623 to Wentorf, Jr. et al., the disclosure of which is incorporated, in its entirety, by reference herein. Optionally, another material may replace the solvent catalyst that has been at least partially removed from the polycrystalline diamond.
Diamond enhanced inserts are frequently used as the cutting structure on drill bits to bore through geological formations. It is not unusual that diamond enhanced inserts are subjected to conditions down hole that exceed the mechanical properties of the insert and failures occur. One factor believed to contribute to such failures is a thermal mechanical breakdown of the polycrystalline diamond structure. In percussive drilling applications, the high frequency of relatively high load impact and rotary actions can generate high temperatures on the tip (contact area) of the polycrystalline diamond inserts. Further, one of ordinary skill in the art will understand that temperatures experienced on a polycrystalline diamond of any drilling tool may be higher than expected or desired.
A percussive bit, also known as a hammer bit, penetrates a subterranean formation through a combination of percussive and rotary interactions with the subterranean formation. A downhole hammer actuates the bit in a vertical direction so that intermittent impacting with the formation, which may pulverize at least a portion of the subterranean formation, may occur. The rotary action may generally be driven by a so-called “top drive” and may facilitate complete excavation of the bottom hole. The inserts on a hammer bit are generally hemispherical or conical in shape. A hemispherical geometry may provide the necessary toughness for a typically brittle polycrystalline diamond material. A variety of polycrystalline diamond insert designs to improve the life of percussive insert are well known in the art. Inventions such as transition layers, non-planar interfaces, composite diamond mixes and non-continuous diamond surfaces are all designed to improve the toughness and overall life of a percussive diamond insert.
The polycrystalline diamond layer generally comprises diamond. However, other materials are often exist due to the nature of manufacturing polycrystalline diamond (“PCD”). More particularly, PCD manufacturing generally requires the presence of a catalyst/solvent metal to enhance formation of diamond to diamond bonding to occur. These catalyst/solvent metal may include metals such as cobalt, nickel or iron. During the sintering process a skeleton or matrix of diamond is formed through diamond-to-diamond bonding between adjacent diamond particles. Further, relatively small pore spaces or interstitial spaces may be formed within the diamond structure, which may be filled with catalyst/solvent metal. Because the solvent/catalyst exhibits a much higher thermal expansion coefficient than the diamond structure, the presence of such catalyst/solvent within the diamond structure is believed to be a factor leading to premature thermal mechanical damage.
Accordingly, as the PCD reaches temperatures exceeding 400° Celsius, the differences in thermal expansion coefficients between the diamond the catalyst may cause diamond bonds to fail. Of course, as the temperature increases, such thermal mechanical damage may be increased. In addition, as the temperature of the PCD layer approaches 750° Celsius, a different thermal mechanical damage mechanism initiates. At approximately 750° Celsius or greater, the catalyst metal begins to chemically react with the diamond causing graphitization of the diamond. This phenomenon may be termed “back conversion,” meaning conversion of diamond to graphite. Such conversion from diamond to graphite causes dramatic loss of wear resistance in a polycrystalline diamond compact and may rapidly lead to insert failure.
Concerning percussive drilling, polycrystalline diamond percussive inserts may be more susceptible to degradation associated with increased temperatures than diamond cutting structures utilized on other earth boring tools (e.g., fixed cutter bits (PDC bits, roller cone bits (TRI-CONE®, etc.). Explaining further, percussive drilling may employ air, foam or mist as a coolant. However, none of such coolants transfers the heat away from the insert tip. Other drilling methods may utilize oil or water-based drilling fluids (e.g., muds) that may be more effective in cooling the diamond structure.
Thus, it would be advantageous to provide a polycrystalline diamond compact or insert with enhanced thermal stability. In addition, subterranean drill bits or tools for forming a borehole in a subterranean formation including at least one such percussive polycrystalline diamond insert may be beneficial.